Really enjoying the summoner, especially blood totems/minions. Blood is everywhere.
They do physical damage and I typically go with a team heavily focused on that type of damage (nothing is immune). The minions are great, especially with the melee infusion (bullrush/whirlwind) and eventually enough totems on the ground that all phys shields are gone asap for my physical bros to mop up. The minions can scamper after any archers or magic users that are being annoying to get hold of and the totems blow down the opposing tank shields.
The blood minion gets its own 'heal' even without infusion, so it has some good survivability while hunting down the stragglers.
The minion infusions are based on the 'class' stats, so the range infusion gets boosted by dex, melee infusion boosted by str, so could see where you might have your tank/archers also spend a point to get access to those minions.
Have not gotten a great handle on the polymorph best usage however. Currently have my ranger using it on the side mostly just for mobility (bull horns and flight), but typically not as much a difference maker in fights like summoner. Still on my first playthrough after patch though, so later skills may make a difference.